1. Field of the Invention
The present invention relates to a wired circuit board and, more particularly, to a wired circuit board having terminals to be connected to external terminals through molten metal.
2. Description of the Prior Art
A wired circuit board usually has terminals to be connected to external terminals as a part of a conductive pattern of the wired circuit board.
Molten metal, such as, for example, solder balls, is often used for connecting the terminals of the wired circuit board to the external terminals. The solder balls are placed on the terminals and are melted on the surfaces of the terminals, whereby the terminals of the wired circuit board are electrically connected to the external terminals through the solder balls.
When the terminals have flat surfaces, the solder balls can roll around the surfaces of the terminals. Prior art proposes an attempt solution that electrodes (terminals) formed on the substrate are provided, at center portions thereof, with cavities to place the solder balls on the electrodes stably (Cf. JP Laid-open (Unexamined) Patent Publication No. Hei 11-266066, for example).
In addition, the prior art proposes a solution that a solder plating layer of ring form is laminated on those electrodes formed in ring form by solder plating, to secure a large connection area for the solder ball (Cf. JP Laid-open (Unexamined) Patent Publication No. Hei 11-266066, for example).
However, in the electrodes formed in ring form described by JP Laid-open (Unexamined) Patent Publication No. Hei 11-266066, the substrate is exposed from lower ends of the cavities. Due to this, when the solder balls are placed in the cavities, electrical connection areas for the solder balls to be electrically connected with the electrodes are ensured only by around the inside of the cavities, so there may be cases where insufficient electrical connection areas are provided for the solder balls.
In addition, when the solder plating layer of ring form is laminated on the electrodes formed in ring form, larger electrical connection areas can be ensured, but such a solder plating layer may be melted accompanied by the melting of the solder balls, then causing, especially when the conductive pattern is a fine pattern, adjacent electrodes to be shorted with the spilled solder.